Cellular communications systems are well known in the art. In a typical cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells,” and each cell is served by a so-called “macrocell” base station. The base station may include baseband equipment, radios and antennas that are configured to provide two-way radio frequency (“RF”) communications with mobile and fixed subscribers (“users”) that are located throughout the cell. The base station may also have backhaul equipment that enables communications between the base station and the core network of the wireless operator. The antennas are often mounted on a tower or other raised structure, with the radiation beam (“antenna beam”) that is generated by each antenna directed outwardly to serve the entire cell or a portion of “sector” of the cell such as a wedge shaped section of the cell in the azimuth plane.
In order to increase capacity, so-called “small cell” cellular base stations have been deployed in recent years. A small cell base station refers to a base station that typically operates at lower power levels and hence has a much smaller coverage area than a typical macrocell base station. Typically, a small cell base station is designed to serve users within a small area, such as, for example, within tens or hundreds of meters of the small cell base station.
Small cell base stations typically employ an antenna that provides full 360 degree coverage (omnidirectional coverage) in the azimuth plane and a suitable beamwidth in the elevation plane to cover the designed area of the small cell. The small cell antenna may be designed to have a small downtilt in the elevation plane to reduce spill-over of the antenna beam of the small cell antenna(s) into regions that are outside the small cell and also for reducing interference between the small cell and the overlaid macrocell.
Small cell base stations may be deployed in a number of different environments. In some cases, small cell base stations are used to provide cellular coverage to high traffic areas within a macrocell, which allows the macrocell base station to offload much or all of the traffic in the vicinity of the small cell to the small cell base station. In other cases, small cell base stations may be deployed within structures such as office buildings, shopping smalls, stadiums and the like to provide coverage within such buildings. Small cell base stations may be particularly effective in this environment as concrete and steel structures may degrade the quality of service within the interior of such buildings when served by a macrocell base station.
Traditional small cell base stations operate in much the same way as a macrocell base station, with each small cell base station including its own baseband equipment, one or more antennas connected thereto (depending upon whether sectorization is used), and its own physical cell identifier and backhaul connection to the core network. This may create difficulties when dense deployment of small cells is required, as might be the case in a downtown urban area. For example, borders between adjacent small cells may experience interference and reduced performance. Hand-offs between small cells can become common, which complicate network control and may negatively impact the user experience. Complex radio planning may also be required to reduce interference between adjacent small cells and between the small cells and nearby or overlaid macrocell base stations.
Enhanced small cell base stations have recently been introduced that can provide improved performance, particularly when dense deployment is required. An example of such an enhanced small cell is the OneCell C-RAN Enterprise Small Cell system sold by CommScope, Inc. of Hickory, N.C., which is referred to herein as the “OneCell system.” The OneCell system deploys a plurality of radio units in the area to be served by the small cell, and configures these radio units to operate as a so-called “super cell” so that to the core network the super cell appears like a traditional small cell that has a single physical identifier and a single connection to the core network despite deploying as many as 64 radio units. The OneCell system also uses virtual sectorization within the cell to provide capacity and coverage where it is needed and when it is needed. This approach can provide significantly enhanced data throughputs while simplifying network planning and operation.